Heat exchanger



p 2, 1952 M. FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 Sheets-Sheet 1 Jam m p 1952 M.FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 Sheets-Sheet 2 p 2, 1952 M.FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 sheet s-Sheet 5 IN VE/V 7-01?MEKFR FREA/Kz S p 1952 M. FRENKEL 2,609,184

HEAT EXCHANGER Filed April 10, 1948 4 Shets-Sheet 4 er my.

Patented Sept. 2, 1952 HEAT EXCHANGER Meyer Frenkel, London, EnglandApplication April10, 1948, Serial No. 20,292 i In Great Britain May 22,1947 7:

This invention relates to heat "exchangers Among the objectsof theinvention are:

1. To p-rovidecons'tructions which ensure that for a heat exchange fluidflowing past the outside of heat exchange elements (e; g.- tubes) theflow-layers should :be so guided that the tem-. perature diiTerencethrought he heat transferring wall be kept high substantially all overthe sur--' face of the heat transferring walL- so that the mean rate ofheat-transfer .per unit area of heat transferring wall-taken over thewhole surface should be high, particularly also for cases Wherethe'fluid' flowing outside the passages' has only'a small; specific heatper unit volume as compared with the fluid flowing inside,-or wherefluid flowingoutside the wall is to have only a small temperature-changeas compared to the fluid flowing inside, without undue increases invelocity of flow. r

' 2. To provide a construction which will enable a heat exchanger totransfer large quantities-of heat with the fluid flowing outside theheatexchange elements, for example, tubes moving-by virtue of' thenatural convection supported by some external moving means (pump, or thelike) or where thel fluid moves by virtue of natural convection only;thus dispensing with the external'moving means (pump, blower, or thelike) without excessive surface area of heat trans: ferring walls. Underthis object would fall, for example, a construction of heat exchangercapable of providing air cooling by means of natural convectionfor largeperformances, without excessi've surface-areas of heat transferringwall. The following considerations illuminate the ideas underlying thisinvention; 7

'A' total mean rate of heat transfer per unit area of heat transferringwall, which is indicative of the overall properties of a heat exchanger,depends on; v p

(1) 'On the difierence between the mean temperatures taken over thewhole effective surface area of heat transferring wallQbetween thelayers of the two fluids flowing in immediate heat exchange proximity toboth sides of the heat trans-' ferring wall; a

(2) n the ratio a between the effective surface-area of heattransferring wall and a total area of heat transferring wall, which isobtained by dividing the volume taken up (not enclosed) by thecomponents of theheatexchanger (in cluding essential partsj such (asheader tanks, guide-walls, and thelike), by the thickness, of the heattransferring wall. 1 Accordingly, apart from making provision for 19claims; (01. 257-227) making said mean temperature difference betweenthe flowing fluids large, this invention .also

makes provision for making this factor a as large.

(as near'to unity) aspossible. V a o Further, consider cases in Whichthefluid flow.-

7 ing outside heat exchange elements: i to' flow due to naturalconvection I only.\ Let for example, layers of thisifluid .belguidedbetween a row of vertical tubular surfaces and a casingsurrounding thesame, forming apassage for said fluid with alarge U/ Aratio, ratioofawetted cire cumference U to flow-'cross-section;A, as is.neces-.

sary if the layer of fluid is,.-to take effective part in the heatexchange. Then,-. as .proved, the natural convection effect. will.increase the velocity of .the layer only up to .acertain height ofpassage, while foraa, passage of any greater height the velocity of flowwill not increase beyond the value attainedatthat limiting height,

due tolthe. friction lossesin,thepassage; This height, up to whichthezvelocity due. to natural.

convection effect still increases, .Idepends .Onthe U/A .ratio, andiinsordercto obtain the benefit, of the. natural convection effect,provision has to. be made to. remove thisfllayer ofcfluid from the heatexchanger pa'ssagecwith the large U/A.,ratio ,at or below this limiting.height, and. to. guide. it into a passage with a smaller Uf/Aratio,-..Where its velocity increases further, .duerito naturalconvectionefiect. A c g .1

Accordingly, in order to achieve-the objects, this invention providesfor means whereby,v at a position along. a flow of a fluid past a heatexchange element in a passage formed, according to thisinvention,i;between a row of such heat exchange elements andalguide-casing surroundingxsame, layers of said fluid which haveattained a required changeof temperature whilejflowing in immediate:heat exchange proximity with said elements are diverted from the heattransferring wall and led. out of said passage, jwhilelayers ofthistfluidwhichhave not yet taken part in the heatexchange andthussubstantially still have their initial temperature, areguided-intoimmediate heat exchange proximity,with, continuations of saidheatexchange-elements. ,This is done in order to-avoidth-at further flowoflayers which have attained their required, temperature in the immediateheat exchange proximity ofthe element should change the'temp'eratureof,these layers too, far, thus reducing the meantempera: ture, differencethrough the heat transferring wall, and further, from the point of viewsof natural convection emotion of the fluid, in order that a layer, offluid which may have been given side heat exchange elements, thusmaintainingthe temperature difference through the heat transferring wallof these elements all along the total surface of heat transferring wall,thereby making high the mean rate of heat transfer per unit area of heattransferring wall, and where this is required, fully exploiting thenatural convection effect for moving said fluid.

In the accompanying drawings, showing some examples:

Fig. 1 is a vertical section through one embodiment of the invention;

Fig. 2 is a plan section along the line II--II of Fig. 1; 3

Fig. 3 is a partial vertical section through a second embodiment;

Figs. 4 and 5 are a sectional front elevation and a part sectional sideelevation respectively of a further embodiment, Fig. 4 being taken online IV--IV of Fig. 5;

Figs. 6 and 7 are a sectional front elevation and a part sectional sideelevation respectively of another embodiment, and Fig. 6 being taken onthe line VI--VI of Fig. 7.

In said drawings like parts are denoted by like reference characters. y

In the embodiment shownin Fig. 1, I denotes a duct which contains aplurality of rows of heat exchange elements such as tubes 2, bathedexternally by a first fluid and traversed internally by a second fluidtaking part in the heat ex-, change- Each of these rows is enclosed by aguide casing 3 having an entry [8 at one end and an exit l9 at the otherend for said fluid. Each row of tubes 2 also debouches into .two headertanks 4 and '5. which .are individual to each row of tubes 2 andrespectively induced into and lead away from said tubes said second heatexchange fluid.

At various positions along each guide casing 3, said casing is providedwith entry slots. 6a and exit slots 6b in opposite sidewalls thereof andrespectively extending the entire width of the casing, and the upper endof the'casing 3 below each entry slot 6a is bent inwards at l to form anentry-guide vane whilst the lower end of the casing 3 above each exitslot 6b is bent inwards at 8 at the side opposite the inwardly bentguide vane I to form a baflie, the portion 8 constituting a continuationof the guide I, the vane thus formed contacting the respective tubes 2round their circumferences. The entry guide means 6a and I of eachadjacent pair of casings 3 are arranged toface each other whilst theexit guide-means 6b and 8 of each adjacent pair of casings are likewisearranged to face each other.

At the entry end of each alternate space l2b between adjacent casings 3into which exit guide vanes 8 lead and which is hence denoted anexitspace, baflie plates 9 are disposed. Each bailie plate 9 carriesside walls I0 which, together with the plates 9 leave exit-spaces 12bopen at their exit ends only. At the outlet end of the other alternatespaces l2a, from which entry guide vanes '1 lead and which are hencecalled entryspaoes, similar baffle plates H are disposedbeiii alternatepairs of guide-casings 3.

4 tween alternate pairs of guide casings 3, said baflie plates 1 Iextending to the walls of the duct l and dividing the space [6a in theduct before entry from space liib after exit.

The aforesaid construction operates as follows:

Assuming that the construction is intended to be used as an air heater,then the entry header tanks 5 will carry a heated liquid, such as hotwater, which flows downwards in the tubes 2, and is led out of the heatexchanger by header tanks 4 after having given its heat to the air.

The air flowing in the portion l6a of duct l flows into eachguide-casing 3 at its lower open end [8, flowing in contact (immediateproximity) to the outside of the tubes and taking part in the heatexchange, and on reaching guide-vanes I is deflected from the heattransferring wall through slots 6b into exit spaces l2b between Inaddition the air flows into every other entry-space 12a betweenalternate pairs of guide-casings 3 from which layers of the air aredrawn through slots ea into contact with the outside of the tubes atdifferent positions along the height of the passage, the respectivelayers being then led out again into exit-spaces [2b. Air coming intothe heat exchanger from below is, however, prevented by bafiles 9 andside walls H] from flowing directly into the spaces l2b, in which flowsair which has already taken its part in the heat exchange and baffle llprevents exit of air, which has not yet taken part in the heat exchange,from the entry-spaces I211. into the space I6?) 1 in the duct l, leavingonly exit holes for the passages 12b into this space, for air which hasbeen heated. Thus the arrangements of walls Ii!v and bafiles 9 and IIprevent air which has not yet been heated from passing from entry-spaces12a. to exit-spaces l2b, and more generally from spaceifia to space [61)except through spaces bringing it into contact with the heattransferring wall..

Thus this construction is seen to effect that layers of the air whichhave flowed in contact with the heat exchanger tubes over such,distances that-they have attained their required temperature, are thenled away from the heat transferring walls, and replaced on thecontinuations of the heat transferring walls by fresh layers of air,which still have the initial airtemperature, so that thereby thetemperature difference between the air on the outside of the tubes andthe hot water inside the tubes is maintained high along the length ofthe flow, instead of falling too far, as would be the case if the samelayer of air remained in contact with the tubes.

Further as regards natural convection, this construction ensures that alayer which has flowed in immediate heat exchange proximity with theheat transferring wall in what is, in effect, a passage with a verylarge U/A ratio of wetted circumference to flow-cross-section, in whichbeyond a small limiting height its velocity due to natural convectioncannot increase any further, is led away from the heat transferring wallinto passage [2b whose U/A ratio is much smaller, so'that there thevelocity can increase further, the natural convection thus beingexploited.

Further, with regard to the uniformity of the heating of the air, layersof air having been heated at the lower end of the tubes where thetemperature difference to the already cooled water. is lower, will, inpassingjup the passage l2b, flow'past the exits 61) at both sides, fromwhich'emerge layers of air .whichhave been.

heated. athigher and higher temperature differences, so that thus theless heated layers of air are mixed with those layers which haveibeen.

heated to higher. temperature, andthe air emerges from the tops ofpassages |2bgwith substantially uniform temperature.

1 The arrangement of the tubes 2 in rows, with each row of tubes havingheader tanks 4 and 5 separately to itself, where the tanks 4 and 5 arestaggered for adjacent rows, ensures that the .air fiows into and. outof the spaces between the rows of tubes without substantial change toflow along the tubes in these spaces between the tubes of the same row,so that by this ,arrangement of separate header tanks for eachrow oftubes, which have 'spacesbetween them in the plane normal. to the'flowdirection ofthe air, as well as in. the flow-direction, even flow. ofthe air is provided at all positions round ;the.

circumference ofeach tube, and all tubes of the heat exchange are madesubject to air flow at the same velocity.

The embodiment illustrated in Fig. 3 is substantially identical withthat illustrated in Figs. land 2, with the following exceptions: Thetubes 2 are each traversed by a smaller-diameter tube l3 which is open.at both ends and passes through headers 4 and 5. The water to be cooledthenflows down the annular spaces between the respective tubes 2 and I3,while cooling air also flows upwards through tubes l3. A further featureby which the embodiment of Fig. 3 differs from that of Figs. 1 and 2 isthat the duct i does not extend beyond the highest peripheral bafflespace, so as to permit free. access of air to'the casings 3 in alldirections i. e.'both vertically and horizontally, the bame plates 9 andH. and sidewalls H) of spacer |2b forming a labyrinthine' bafilepreventing any direct access of air to the spaces |2b traversed by airwhich has already taken part in the heat exchange. A further differencebetween thepresent embodiment and that described with reference to Figs.1 and 2 is that the duct I terminates in -a chimney ll .of a substantialheight depending on requirements, the function of the chimney being tocreate an updraught and produce extra velocity past the heattransferring walls. -A section is shown between two tubes of a row.indicating air flow there, and a further section through the centreplane of a tube 2, indicating water flow by arrows .in the annularspace. between tube 2 and the inner tube l3, carrying cooling air. w i YFigs. 4 and'5 show another embodiment in which, instead of one row oftubes comprising vertical tubes 2 running from entry header tank 5' forthe-hot water at the top to exit header tank 4 at the bottom, there areprovided two rows of tubes in the same plane. The top row of tubes isexactly the same as described with reference to Figs. 1 and 2, exceptthat the inner tubel3 in each tube 2 is missing. At the posi- 6 tionswhere tubes 2 enter their bottom header tankx3 tube stumps. 32 ofsmaller diameter than; the. tubes 2 are inserted into the mouths oftubes 2,

these stumps 32 continuing through headertanks' 3| to form a row oftubes whichis again surrounded by a; guide-casing3, similar to the upperrow of tubes 2. Tubes 32 at their bottom ends debouch into header tanks33 for the water. The arrangement of the guide-casings 3with their entryand exit slots 6a and 6b and the entry.

and exit passages [2a and [2b formed between them is analogous to thatdescribed with reference to Figs. 1 and ,2, with the addition thatbaiiles and 42. connecting to tank 3| in spaces |2a and |2b respectivelycooperate with bafiies and9 respectively to separate spaces containing.

air which has not yet taken part in the heat exchange from spacescontaining air which hasv taken part in the heat .exchange.

The aforesaid construction operates as follows: Hot water enters tubes 2of the top row through header tanks 5 from duct 36 and while. flowingdown the tubes 2 the. outer layers of hot water.

in the tubes give up heat to the layers of unheated air which aresuccessively guided into contact with the heat transferring wall byguide-casing 3,.as described with reference to Figs. 1 and 2.

Before the water enters the intermediate header tank 3|, tubestumps 32separate the inner layers of the flow in each tube, which havesubstantially retained their original tempera-:

ture,.from the outer layers, which have become cooled, and these outerlayers flow into the intermediate header tank 3| and are led from thereout of the heat exchanger in duct 34. Meanwhile the still hot-innerlayers of water flow down tubes 32,.where they come into heat exchangeproximity withunheated layers of air brought to the heat transferringwall by guide-casing 3 as already described, before being led out of theheat exchanger. in header tanks 33, debouching into. collector '35.

Figs. 6 and 7 show a further embodiment, the top of which comprises rowsof tubes 2 between top header tanks 5 and intermediate header tanks 3|,the rows of tubes being surrounded-by guide-casings 3, similarly asdescribed with reference to Figs. 4. and 5.

The stumps 32 are inserted into the mouths of tubes 2 before these entertheir intermediate header tanks 3|, and pass through tanks 3| and leadinto a header tank 3'|. From this header tank 31. anew row of tubes 38begins, the tubes of this row as seen in Fig; '7 not being on the samecentre-lines as the tubes-2 of) the row above, but being staggeredrelatively thereto, the centrelines, however still lying in the sameplane. These tubes 38 lead into exit header tanks 33, and are traversedby internal tubes 39 which pass through both header tanks 31 and 33. Therow of tubes 38 is surrounded by a guide casing 3, as previ ouslydescribed. A baffle 40 is provided between the intermediate header tanks3| and 31 of a row and baiiles 4| and 42 in spaces |2a and I2!)respectively. operates as follows:

Hot water'coming from duct 36 is led through header tanks 5 into tubes 2of a top row, and while flowing down tubes 2, the outer layers of thewater in the tubes give up heat to the unheated layers of air which aresuccessively guided into contact with the heat transferring. wall byguide-casing 3. as described with reference to Figs. 1 and 2. Tube stump32 separates the outer layers of the water, which have taken their partThe. aforedescribed construction diateheaders 31; whence they-flow outof the heatiexchangerthroughscollector 3 Lv y iThezi'nner layers'fof the:water, whichihair'e substantially. retained their originaltempera'ture.are

led into" intermediate header. tank .31 from where it flows inirtheannular spaces between tiibes'38 and:39.down to header tank. 35. :Air.flows along the :outside of tubes 38, beingl'guided infgiudecasing 3,aspreviously.- rde'scribed xand'rflows through the inner tubes i39,'. totake part in the heat exchange. Battles K ibe'tweengthe intermediateheaders 3| and-.31 guide'theair; which has flowed through the innertubes-39, intothe spaces 12b for; air which hasutakenits part in, theiheat exchange, forming witlribailies .41, '42 and l I, '9 the system ofbafiles which, together withrside walls H) of spaces 'l2cipreventsanyair which has notyet taken part in the :heat exchange fromenteringssaid spaces l2b.

In both the embodiments described with reference toFigs. 4 'and.5 toFigs; (Sand 7, a duct will surround the assembly, the'functionof theduct being the same as thosezof :the duct described with" reference toFigsl and 2 for a'forced convection heat exchanger, or as described withreference to Fig. 3 for a'natural"convection'iheat exchanger. :Boththese embodiments :willbe'suitablefor applications where thezfluidflowing iiII-' side the tubes is to be divided into two separatequantities, each of which "has to experiencea differentv temperaturechange.v

In the examples described, it will have been noted that the surfaces onwhichurespectively are situated the. centre-lines of :the .tubes'ofarow, which surfaces may, according to thisinvention be closed inthemselves, as,-:for$ example, cylinders, have'generating lines whichare'sub which would arise due to centrifugal forces act-1 ing at changes'of the flow-direction, and which would reduce the effective'iarea ofheat :transferring wall for heat exchange,

'.(3): In "order that, quite generally, theflow-f path of the i'fluidfrom the entry t9 ith'e 'hea't X: changer to the exit from t heatlegchangeri.

should b'e shortest, and v I (4) In order to keep the :cross-sectionala'rea normal to the flow-direction of ithe duct which surrounds thewhole. assembly, in lflSLl-Slilfiill !a ratio as possible to the actualtotal .cross-section of'thisffluidtinto theiispaces between ftherows oftubes (and similarly the ratio betweenwthecross-section for the fluid inthe :du'ct after theheat exchanger to the actual totalzexitcross-sections of the fluid from the passages betweenrows of tubes) sothat'pressure :losses due to sudden changes of cross sectionaliarea ofiflowzarek eptf as low as possible. Y

Thus, in-embodiments of ithe inventionthefluid flowing outside thepassages (tubes) :willvbe guided by guide-walls ,andaguide-vanesfin'snch a way,;-that for the periods that layers of- ,thisfluid' 8 areactua'lly taking direct part in'the heat exchange, i. 'e. are in contactwith the-'heat'transferring wall, :the centres of gravity of.these'layers anywhere along their flow in contact with he'attransferring .ivall} are on substantially straight lines I I In order toprovide for layers being led away' from the heat transferring'wall whenthey have taken their part in the heatexchange, and other layers, whichhave not yet been in contact with heat transferring wall, being led intocontact with heat transferring Wall, each row of tubes is provided witha guide-wall substantially surrounding it, and openat either end toallowlentry and exit for the fluid flowing outside the tubes.Theseguidewa'lls, at difierent positions along the flow'of thefiuidlayers in contact with a heat transferring wall, 'will'have slotsrunning normally to this flow direction, or other suitable openings, toprovide exits and respectively'em tries for-suchlayers. 'In preferredembodiments, using the same guide-vane to lead layers of fluid away froma heat transferring wall with its one side and otherlayers .into contactwith a con- I tinuatlon of heat transferring wall with'its other side,the exits forthe fluid layers whichhave takentheir partintheheat-exchange are arranged-to one side of this row ofltubes, while theentries for the fluid layers which have not yet'taken part 'in the heatexchange are arranged onthe other side of this row ofit'ubes.

The rows oftubes making up a heat exchanger,v

with their surrounding guide-casings, will in preferred embodiments beso arranged relatively to one another, that the entries for adjacentrows of tubes face one" anoth'erzacross aspace between the guide-wallsof these rows, andosimilarly the exit slots ofa'cljacent rows of tubesface one another across another such space between two guidewalls.Accordingly, every second space between adjacent rows of tubes will-havefluid flowing in. it which has not yet :been in contact with'a heattransferring'wall, which is being :led off inlalyers to therows of heatexchange, elev mentszateitherjside' to come into contact with-aheatztransierrin'g wall at different positions along the fiowiiof suchlayers, while every :other second spacew'ill have fluid-flowing in itwhich has already taken its part in the heat e hansa. h v ing beenguided into said space from both rowsof tubes atidifierent positions.The walls forming the spaces carrying fluid which has already't'aken itspart the-heat exchange :will be so closed,

that nolayers 'of fluid whichha've 'not been in 1 contact :with a :heattransferring wall can enter into:siichwspacessi I .In::-:prfefer'redembodiments of this invention, the generating linesaof :the: centre-linesurfaces of adjacent-wows 10f? tubes will ,be somewhat inclinedto'oneuanctheryso that passages between rows of tubes which c'arryxfiuidwhich. has not yet taken :;part :inithe'rheat exchange and is led awayalongthetlengtliof the passages .get narrower in the flow-direction:while the passages carrying change get wider in the flow direction;

' In construction of the heat exchangers in accordance with the;invention, \difiere nt positions on the-heat transferring wall or wallsalong the flow- .of. the; fluid :flowin'g outside the passages or tubes,are :brought :into contact with different layers'of thisfluid,*WhiChfhtlVB notyet taken part in the heat-exchange, and in this way;one and the same ."volume ofv thei fluid flowing inside the passages 01'tubes; will .in "its passage through the attain tubes, come into heatexchange proximity in consecutive intervals of time with layers of theoutside fluid, which have not yet taken part in the heat exchange andthussubstantially still have their initial temperature, so that in thisway the temperature difference through the heat transferring wall iskept high particularly for special cases where in the fluid inside thetubes has the 7 high specific heat per unit volume, while the outsidefluid has a low specific heat per unit volume, without velocities beingincreased, and in this losses of the fluid flowing outside the tubes;from the pointof view of bringing about effective heat exchange betweena liquidof high specific heat per unit volume inside the tubes'an'd airoranother gas fiowing outside the tubes, where this gas has a very muchsmaller specific heat per unit volume (for'the'cases of water inside andair outside the tubes, the'ratio of the specific heats per unit volumemay be'about 3000-to 1) and finally from the point of view of efiicient'exploitationof the natural convection as moving agent for the coolingair, leading e. g. toeconomical designs of coolers of large capacitywithout fan-draught for the cooling air, and making'atmospheric airapplicable as cooling agent instead of water for certain-applications.

It will be understood that the embodiments of my invention described inthe foregoing are by way of example only, and that many other examplesand modifications of the invention are possible within the scope of theappended claims.

1. In and for a heat exchanger the combina tion of a row of heatexchange elements respectively bathed externally by a first fluid andtraversed internally by a second fluid taking part in the heat exchange,of a guide-casing for'said first'fluid around said ro'w of heat exchangeelements with an entry for said first fluid at one end and an exit forsaid first'fluid at its other end, and

of an entry guide means and an exit guide-means in-the walls of saidguide-casing situated between the entry and exit ends of saidguide-casing, at a position along the length of at least one of the heatexchange elements of said row, for diverting at least a layer of saidfirst fluid which has flowed in immediate heat exchange proximity withonly a part of said one element and has taken its part in the heatexchange, away from said element to outside said casing, and for guidinga layer of said first fluid, which'has flowed outside said guide-casingand has not'yet been in contact with a heat exchange element intoimmediate heat exchange proximity at least with said one heat-exchangeelement of said row on its continuation to flow therealong in the samedirection in which flowed the layer which has been diverted from'saidelement.

2. In and for a heat exchanger, the combination as claimed in claim 1,in which said entry and exit guide-means are in direct contact with atleast said one heat exchange element of said row.

3. In and for a heat exchanger, the combination as claimed in claim 1,in which said entry and exit guide-means in the walls of saidguideleasing arerespectively disposedalong the entire "width of saidguide-casing on opposite side-walls thereof. 7 V 4. In and for a heatexchanger, the combination "as claimed in claim 1, in which said entryand exit guide-means comprise slots in opposite sidewalls of saidcasing, said slots extending respectively the entire width of saidguide-casing, and a vane connecting one edge of the entry-slot with 10the other edge'of the exit-slot in a gradual transition, said guidevvanegradually di-verting with Lone side-surface layers of fluid, which haveflowed in immediate heatexchange proximity substan- {tially alongsaidheat exchange elements or said row and have taken their part in theheat exchangeto outside said guide-casing'on one side,

and said guide-vane with its opposite side-sur- Lfacefgui ding layers offluid, which have flowed ,o'utsidesaid guide-casing on its other sideand have not yet been in heat exchange proximity with a heat exchangeelement into immediate heat exchange proximity with said elements ofsaid row on'the'ir respective continuations.

' 5. In and for a heat exchanger, the combination of a'plurality of rowsof heat exchange eler'nents, which arerespectively bathed externally bya first fluid and traversed internally bye. second fluid taking part inthe heat exchange, of

a plurality of guide-casings for said first fluid, each arranged arounda row of said elements, and having each an entry for said first fluid atone end and an'exit for said first fluid at its other end, and ofatleast one entry guide-means and exit guide-means for said first fluid inopposite sidewalls and situated between the entry and exit end of saidcasing at a position along the length of said heat exchange elements ofsaid row, for diver-ting layers of said first fluid which have flowed inimmediate heat exchange proximity substantially along the elements ofsaid row and have taken their part in the heat exchange away fromsaid'elements'out of said casing to one side thereof, and for guidinglayers of said first fluid which have flowed outside said guide-casingon itso'ther side and have not yet flowed in heat exchange proximitywith a heat exchange element into immediate heat exchange proximity withsaid elements of said row on their respective continuationsto flowtherealong in the same direction in which flowed the layers which havebeen diverted from said elements, said rows of heat exchange elementswith their guide-casings being spaced adjacent one another so that foradjacentrows said entry and respectively exit guidemeans face oneanother across alternate spaces between guide-casings of adjacent rowsof elements, each alternate space between two guidecasings into whichface exit guide-means thus forming an exit-space and containing saidfirst fiuid'iwhich. has already taken part in the heat exchange, andevery other alternate space between two such guide-casings into whichface entry guide-means thus forming an entry-space and containing saidfirst fluid which has not yet taken part in the heat exchange, the saidcombination further comprising side-walls at least for said exit-spaces,which side-walls extend between adjacent guide-casings, and bafllessituated substantially at one end of said space for at least saidexit-spaces, for separating said exitspaces from said entry-spaces.

6. In and for a heat exchanger, the combination as claimed in claim 5,in which said heat eX- change elements have entry and exit header tanksrespectively common to each row for said 11 second fluid flowinginternally through said heat exchange elements and taking part in the;heat exchange. I 7. In and for a heat exchanger, the combinationasclaimed in; claim 5 in which said heat exchange elements, are tubeshaving entry and exit header tanks respectively common. to each; row

rality-of, rows of heat'exchang e elements. within said duct, saidelements being respectivelybathed externally by-a firstfluiditraversingsaid duct and traversed internally'bya; second fluidtaking part in-the heatexchange; 'apluralityof guide casings for saidfirst fluid each-arranged around a rowof said elements and having eachan entry forsaid first fluid at one end: and an exit for saidflrst fluidat its other end, andat least one entryguide-means and exit,guide-means; for said first fluid in opposite side-walls andsituatedbetween the entry and-exit ends of; said casing at a position along thelength ofsa-idheat exchange'elements of said r0w,--for,divertinglayers-of said first fluid which have flowed in' immediateheatexchange proximity substantially along the elements of said row' andhave taken their part in the heat'cxchange away from said elements outof said casing to one side thereof, and for guiding layers of saidifirstfluid which have flowed outside said guide-casing onits other side andhave not yet flowed. inheat exchange proximity with a heat exchangeelement into immediate heat exchange proximity with said -elements ofsaid row on their respective continuations, to flow. therealcng in thesame directionin which flowed the layers which have been diverted fromsaid elements, said' rows of heat exchange elementszwith-theirguide-'casingsbeing spaced adjacent to one another so that foradiacentrows said entry and respectively 5 exit guide-means face oneanother across alternate spaces between guide-casings of adjacent rowsof elements, each alternate space between two guide-casings, into whichface exit guide-means thus forming-Jan exit-space and containing, firstfluid which has already taken part in the heat exchange; and every otheralternate space between two-such guide-casings, into which face entryguide-means, thus'forming an entry-space containing first fluid whichhas not yet takenpartin the heat-ex change, the said heat exchangerfurther comprisi ing the side-walls at-least for said exit-spaces, whichside-walls extendbetween adjacent guidecasings, and baffles. situatedsubstantially at at least one. end of said exit and entry spaces,- thesaid bafiies at the ends of said entry-spaces extending to the wall ofsaid duct, for separating space in said duct which contains said firstfluid before it has taken part in the heat exchange from spacein saidduct which containssaid first fluid after it has taken part in theheatexchange.

9. A heat exchangeras claimed in claim 8,.in which the surfacescontaining the middle-lines of the heat exchange elements ofsaidrowshave substantially vertically directed generating lines,

and in which said duct surrounding the assemoly ends in a chimney, thesaid first fluid flowin through the said heat exchanger by virtue ofnatural convection only.

10. A heat exchanger asclaimed in claim 8, in which said heat exchangeelements are tubes having entry and, exit header tanks respectivelycommon to each row of tubes for said second fluid flowing. internallythrough said tubes and taking ,part in theheat exchange, said. entry andrespectively exit header tanks for every adjacent pair ofrows being.disposed in staggered relationship to. one another, and the-surfacescontaining the middle-lines of the heat exchanger-tubes of said rowshaving substantially vertically directed generating lines, andsaid ductsurrounding the assembly ending in a chimney, the said firstfluidflowing through the heat exchangerby virtue of natural convection only.

11. A heat exchanger comprising at least two sets of rows of heatexchange elements, 1 each forming a heat exchanger as claimed in claim8, arranged one. after theother inthe flow.- direction of saidflrst'fluid withsaid-duct' common toboth, the saidheat-exchange elementsbeing tubes ofstep-wise increasing diameters "for consecuti-ve rows oftubes of'the said sets, a'header tank disposed betweenjand common toeachtwo such consecutive rows of tubes, the tubes of the rows oflarger'diameter' tubes debouching thereinto and the smaller, diametertubes of the consecutive row passing therethrough into the mouths of thelarger-diameter tubes of said firstmentioned row, said header tanksserving to'lead away out of the heat exchanger the outer layers of thesecond fluid flowing inside said tubes of said consecutive rows fromsaid larger'diameter tubes tosaid smaller diameter tubes, while theinner layers of said fluid continue to flow inthe smaller diameter tubesof'the consecutive row.

12. A heat exchanger comprising two sets of rows of heat exchangeelements, each'forming a heat exchanger as claimed in claim 8', arrangedone after the other in the flow direction of said first fluid with thesaid. duct common to both, the said heat exchange elements of each rowbemg tubes having entry and exit header tanks respectively common toeach row of tubesfor said second fluid flowing internally therethrough,said heat exchanger further comprising smaller diameter tube-stumpspassing from the mouths of; the tub-es of a row through the exit headertanks of this row into the entry header tanks of the consecutive row oftubes, the outer layers of the flow of saidsecond fluid in the tubesof'said first-mentioned row flowingoutside said" tubestumps into theexit header tank of this row, which leads them out of the heatexchanger, while the inner layers of flow of the second fluid in therespective tubes flow through said tubestumps into the entry header tankof the consecutiverow of tubes, the tubes of said consecutlVe' row beingon centre-lines different from those of the tubes of the first rowand'being provided with smaller diameter inner tubes which pass throughthe entry and exit header tanks of this row, the annular spaces betweensaid tubes and said inner tubes of said row being traversed by saidsecond fluid taking part in the heat exchange, while the inner tubesthemselves are traversed by said first fluid which also bathesexternally the tubes of all rows, said heat ex changer furthercomprising bafiies' between the exit header tank of one row of tubes andthe entry header tanks of the consecutive row of tubes, for guidinglayers of said first fluid which have flowed through said smallerdiameter inner tubes of a row into the exit space formed between theguide-casing of this and of a laterallv ad acent row, said bafilesfurther serving to sepa ratesuch exit-spaces, in which flows fluidwhich" "'13 has taken part in theheat exchange from entry spaces whichcontain first fluid which has not yet taken partin the heat exchange. 13

1 3 A heat exchanger comprising a duct, a row of. heat exchange elementsrespectively bathed externally by first fluid traversing said duct andtraversed internally by a second fluid taking part in the heat exchange,a guide-casing'for said first fluid around said 'roW'of' heat exchangeelements with an entry for said first fluidsa-t'bne end and an exit forsaidfirst fluid at itsfother end, andan entry guide-meansand anexityguidemeans in the walls of said guide-casing and situated betweenthe entry and exit ends thereof, at a position along the length of atleast one of said heat exchange elements of said row, for diverting atleast a layer of said first fluid which has flowed in immediate heatexchange proximity with only a part of said one element and has takenits part in the heat exchange, away from said element to outside saidguide-casing, and for guiding a layer of said first fluid which hasflowed outside said guide-casing and has not yet been in contact with aheat exchange element into immediate heat exchange proximity at leastwith said one heat exchange element of said row on its continuation, toflow therealong in the same direction in which flowed the layer whichhas been diverted from said element, the said heat exchanger furthercomprising baiiles connecting said guide-casing and the wall of saidduct for separating space in said duct and outside said guide-casingwhich contains first fluid before it has taken part in the heat exchangefrom space in said duct and outside said guide-casingwhich containsfirst fluid which has not yet taken part in the heat exchange.

14. A heat exchanger as claimed in claim 13, in which said entry andexit guide-means comprise slots in opposite side-walls of saidguidecasing, said slots extending respectively the entire width of saidguide-casing, and a vane connecting one edge of the entry-slot with theother edge of the exit-slot in a gradual transition, said guide-vanegradually diverting with one side-surface layers of fluid, which haveflowed in immediate heat exchange proximity substantially along saidheat exchange elements of said row and have taken their part in the heatexchange, to outside said guide-casing on one side, and said guide-vanewith its other side-surface guiding layers of fluid which have flowedoutside this guide-casing on its other side and have not yet been inproximity with a heat exchange element into immediate heat exchangeproximity with said elements of said row on their respectivecontinuations.

15. A heat exchanger comprising a duct, a plurality of rows of heatexchange elements within said duct, said elements being respectivelybathed externally by a first fluid traversing said duct, and traversedinternally by a second fluid taking part in the heat exchange, aplurality of guide-casings for said first fluid, each arranged around arow of said elements and having each an entry for said first fluid atone end and an exit for said first fluid at its other end, and at leastone entry-guide-means and an exit guidemeans for said first fluid inopposite side-walls and situated between the entry and exit ends of saidcasing at a position along the length of said heat exchange elements ofsaid row, for diverting layers of said first fluid which have flowed inimmediate heat exchange proximity substantially along the elements ofsaid row and have taken their part in the heat exchange away from saidelements out of said casing to one side thereof, and for guiding'layers*of said first fluid which have flowed outside said guide-casing "on itsother side and 'havenot yet flowed'irl heat exchange proximity with aheat exchange 'ele meiitl'*into immediate' heat exchange proximity withsaid elements of said row on their respective continuations, to flowtherealong in the same direction in which flowed the layers which havebeen diverted from said elements, said rows of heat exchange elementswith their guide-casings being spaced adjacent to one another so thatfor adjacent rows said entry and respectively exit guide-means face oneanother across alternate spaces between guide-casings of adjacent rowsof elements, each alternate space between two guide-casings into whichface exit guide-means thus forming an exit-space and containing firstfluid which has already taken part in the heat exchange, and every otheralternate space between two such guide-casings into which face entryguide-means thus forming an entry-space containing first fluid which hasnot yet taken part in the heat exchange, the said guide-casingsextending up to the walls of said duct, and the said heat exchangerfurther comprising baffies situated substantilly at at least one end ofeach of said spaces and extending between adjacent guide-casings and upto the wall of said duct, for separating space in said duct whichcontains first fluid before it has taken part in the heat exchange fromspace in said duct which contains first fluid after it has taken part inthe heat exchange.

16. A heat exchanger as claimed in claim 15, in which the surfacescontaining the middle-lines of the heat exchange elements of said rowshave substantially vertically directed generating lines, and in whichsaid duct surrounding the assembly ends in a chimney, the said firstfluid flowing through the heat exchanger by virtue of natural convectiononly.

1'7. A heat exchanger as claimed in claim 15, in which said heatexchange elements are tubes having entry and exit header tanksrespectively common to each row of tubes for said second fluid flowinginternally through said tubes and taking part in the heat exchange, saidentry and respectively exit header tanks for every adjacent pair of rowsbeing disposed in staggered relationship to one another; in which thesurfaces containing the middle-lines of the heat exchanger elements ofsaid rows have substantially vertically directed generating lines, andin which said duct surrounding the assembly ends in a chimney, the saidfirst fluid flowing through the heat exchanger by virtue of naturalconvection only.

18. A heat exchanger as claimed in claim 15, in which said heat exchangeelements are tubes having entry and exit header tanks respectivelycommon to each row of tubes for said second fluid flowing internallythrough said tubes and taking part in the heat exchange, said entry andrespectively exit header tanks for every adjacent pair of rows beingdisposed in staggered relationship to one another.

19. A heat exchanger as claimed in claim 15, in which said heat exchangeelements are tubes having entry and exit header tanks respectivelycommon to each row of tubes, said tubes being traversed by smallerdiameter tubes passing through the header tanks of said row of tubes,

15 said header tanks serving: the annular spaces between said: outer andinnertubes with said second fluid taking part ,in-the-heatr. exchange,said first; fluid taking part in the heat exchange also flowing throughsaid'smaller diameter, inner 5 tubes. MEYER FRENKEL.

, REFERENCES; CITED "The following references are of record. in the 10file of this patent: I

Number Number UNITED STATES PATENTS Name I Date McGregor Mar. 25, 1924Smith Dec. 1'7, 1929 Jacocks Feb. 2% 1931 FOREIGN PATENTS Country DateGreat Britain Oct. 28, 1926 Great Britain June 29, 1933 Germany Oct. 10,1917 Germany' Mar. 23, 1935

